1. Field of the Invention
This specification relates to amorphous carbon nanofibers and copper composite nanoparticles. The amorphous carbon nanofibers are including nanoparticles which is including copper component, and the nanoparticles including copper component may be copper nanoparticles or copper alloy nanoparticles. The copper composite nanoparticles, whose surfaces of the nanoparticles including copper component are partially or wholly coated with amorphous carbons, are prepared by grinding the amorphous carbon nanofibers.
This specification relates to a dispersed solution including the copper composite nanoparticles, and preparation methods thereof.
The copper composite nanoparticles may be used to form a thin film on a substrate by printing, and may be used as a functional ink material.
2. Background of the Invention
Recently, a printed electronics industry based on printing technology for producing electronic devices with a thin thickness and low costs has been attracted much attention. Printed electronics technology is used to form a thin film by printing a functional ink material on a substrate, and to prepare various types of electronic devices therefrom. This printed electronics technology is suitable for producing electronic products such as flat or flexible displays, organic solar cells/semiconductor devices, memory devices and next generation mobile IT devices and energy storing and/or generating devices including thin film Li-secondary batteries.
In order to prepare printed electronics devices using a printing processing technique on a plastic substrate, functional nano ink having an excellent dispersion property has to be prepared. Especially, conductive ink utilized for wirings and patterns printed on a circuit board is required to have a uniform particle size and an excellent dispersion property. Since the plastic substrate is easily deformed even at a low temperature, a high-temperature thermal treatment cannot be performed. Accordingly, a basic conductivity of nano ink has to be high enough for an excellent conductivity even by a low-temperature thermal treatment. As a general conductive ink, silver, copper, alloy thereof, carbon nanotube, etc. are being widely used. So far, silver having a high oxidation stability and capable of easily synthesizing nanoparticles is being used the most widely. And, copper ink is also being developed actively for low costs of ink. However, the copper is easily oxidized in the air. Accordingly, required is developing copper ink having high reliability, the copper ink capable of minimizing oxidation of copper particles and having a high electrical conductivity after a printing process.
In order to prepare nanoparticles having a size less than 50 nm, nanoparticles are formed from a metal salt solution in a bottom-up manner. This method is advantageous in that nanoparticles can be directly prepared into solution ink due to a synthesis in a colloid solution. Alternatively, nanoparticles are prepared by grinding bulk powder in a top-down manner. In this case, it is difficult to grind the bulk powder in a size less than 50 nm, and many mechanical stresses are introduced into particles during a grinding process. This may lower unique features and functions of the nanoparticles. However the top-down method is more advantageous in the aspect of massive productions. Accordingly, required is a novel processing capable of minimizing introduction of stresses into particles during a grinding process, and capable of massively preparing copper nanoparticles and copper alloy nanoparticles.
Furthermore, the conventional copper particles have surfaces oxidized by oxygen, thereby having a shape that a thin film such as CuO or Cu2O encompasses the copper particles. This oxide film greatly degrades an electrical conductivity of the copper particles. Accordingly, it is important to prepare nanoparticles capable of minimizing oxidation of copper particles.